Restore sketchy dependency to quick.bin.

Apparently we cannot run at all without the continuations
classes on the classpath. At least that it was I conclude
from the fact that quick/bin/scala hasn't worked since
I routed the plugin classes into continuations-library.

This restores them to quick's classpath so we can have
qscala again.
Merge pull request #2254 from paulp/pr/buildxml

Restore sketchy dependency to quick.bin.